The decline in muscle mass and strength that occurs with advancing age has been associated with physical frailty and a loss of independence in old people. The lack of skeletal muscle activity is a major contributor that is potentially preventable with an appropriate exercise intervention. This research proposal has two specific objectives: l. To determine if the loss of muscle mass that typically occurs with advancing age (78+ yr-old women and men) is associated with a decrease in the rate of myosin protein synthesis or an increase in the whole body or myofibrillar protein breakdown rates. 2. To determine if 2 wk of weight lifting exercise increases the myosin protein synthetic rate or reduces whole body or myofibrillar protein breakdown rates in 78+ yr-old men and women to the same extent that it does in 22-32 yr-old women and men.